We had the same situation in our school a year ago.
New child very violent and aggressive to her classmates. Moved to our school for unknown reasons but clearly struggling.
Yes, my child was pushed, shoved, had things taken off her. I did speak to the school asking them to watch my child.
Yes, most incidents happened during lunchtime when the children outnumber the midday staff and can't concentrate on certain children.
But a year on everything is different, the new child is fully integrated in the class and displays none of the behaviour she did on arrival.
Differences for this child being as follows.
She has a good supportive family who were working with the school, your child now has foster parents to fight for the child you are talking about.
Our school worked with the new child, certainly some things were noticed by my child. Time outs with activities, certain fidget chewey which seemed to reduce the biting. I am sure a massive amount of support was given which we are unaware of.
I asked the child around for tea, hopeing to encourage positive interactions under my supervision. Play dates were hard work but positive.
As a small community we tried to welcome her mum and although in the early months the childs name came up in conversation, it was more with frustration that we worried the school was not protecting our children well enough.
This situation can be turned around but only if you all pull together in the same supportive direction.
Don't gossip about this child, it is not relevant that she is in foster care.
Invite the child home for tea try and see if building friendships at school help the situation.
Talk to the school from the 'protect my child' point of view but be patient.
Be positive, our school does not have a lot of resources but they managed to help the new pupil at our school and there is every reason that the child at your school can settle in too.
Good luck, I know how hard things are when your child comes home reporting an injury or damage to her belongings.
Be positive, be kind, I am hopeful that next year you will be able to post a positive update.